Michael Borsche

Prospects of the EPS GRAS Mission For Operational Atmospheric Applications

Abstract Global Navigation Satellite System (GNSS) Receiver for Atmospheric Sounding (GRAS) is a radio occultation instrument especially designed and built for operational meteorological missions. GRAS has been developed by the European Space Agency (ESA) and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) in the framework of the EUMETSAT Polar System (EPS). The GRAS instrument is already flying on board the first MetOp satellite (MetOp-A) that was launched in October 2006. It will also be on board two other MetOp satellites (MetOp-B and MetOp-C) that will successively cover the total EPS mission lifetime of over 14 yr. GRAS provides daily about 600 globally distributed occultation measurements and the GRAS data products are disseminated to the users in near–real time (NRT) so that they can be assimilated into numerical weather prediction (NWP) systems. All GRAS data and products are permanently archived and made available to the users for climate applications and sc...

Atmospheric temperature change detection with GPS radio occultation 1995 to 2008

[1] Existing upper air records of radiosonde and operational satellite data recently showed a reconciliation of temperature trends but structural uncertainties remain. GPS radio occultation (RO) provides a new high-quality record, profiling the upper troposphere and lower stratosphere with stability and homogeneity. Here we show that climate trends are since recently detected by RO data, consistent with earliest detection times estimated by simulations. Based on a temperature change detection study using the RO record within 1995―2008 we found a significant cooling trend in the tropical lower stratosphere in February while in the upper troposphere an emerging warming trend is obscured by El Nino variability. The observed trends and warming/cooling contrast across the tropopause agree well with radiosonde data and basically with climate model simulations, the latter tentatively showing less contrast. The performance of the short RO record to date underpins its capability to become a climate benchmark record in the future.

Pre-Operational Retrieval of Radio Occultation Based Climatologies

CHAMPCLIM is a joint project of WegCenter/UniGraz and GFZ Potsdam. The overall aim of the project is to exploit the CHAMP (CHAllenging Minisatellite Payload for geoscientific research) radio occultation (RO) data in the best possible manner for climate monitoring. This paper focuses on describing the pre-operational status and technical aspects of the CHAMPCLIM processing system at WegCenter/UniGraz. For creating RO based climatologies we ingest, on the one hand, the complete CHAMP RO dataset provided by GFZ at excess phase level (GFZ level 2, ∼180 profiles/day), which is processed to obtain atmospheric profiles of refractivity, geopotential height, and temperature (in future also humidity). On the other hand, we use operational atmospheric analysis fields from the European Centre for Medium-Range Weather Forecasts (ECMWF), at T42L60 resolution, as reference for quality control and evaluation. For delivering climatologies operationally, which will be prepared at monthly, seasonal, and annual time scales, our aim is to provide them with a delay of at most two weeks after the last measurement (e.g., JJA 2003 seasonal climatology available by September 14, 2003, latest). The climatologies are set up in overlapping equal-area and non-overlapping almost equal-area grids. In order to monitor the error characteristics of the climatologies, various types of error statistics (vs. ECMWF analyses) are performed. The main emphasis of this paper lies on processing the complete 2002–2004 data — starting from March 2002 when the CHAMP data stream became stable and quasi continuous — and on creation of climatologies including error estimates. The spatial set up of the climatologies, exemplary seasonal climatologies (as far as processed) as well as preliminary climatological error estimates are presented.

Global Climatologies Based on Radio Occultation Data: The CHAMPCLIM Project

The German/US research satellite CHAMP (CHAllenging Minisatellite Payload for geoscientific research) continuously records about 230 radio occultation (RO) profiles per day since March 2002. The mission is expected to last at least until 2007, thus CHAMP RO data provide the first opportunity to create RO based climatologies on a longer term. CHAMPCLIM is a joint project of the Wegener Center for Climate and Global Change (WegCenter) in Graz and the GeoForschungsZentrum (GFZ) in Potsdam. It aims at exploiting the CHAMP RO data in the best possible manner for climate research. For this purpose, CHAMP excess phase data provided by GFZ are processed at WegCenter with a new retrieval scheme, especially tuned for monitoring climate variability and change. The atmospheric profiles which pass all quality checks (∼150 profiles/day) are used to create climatologies on a monthly, seasonal, and annual basis. Here, we focus on dry temperature climatologies from the winter season (DJF) 2002/03 to the summer season (JJA) 2004, obtained by averaging-and-binning. The results show that useful dry temperature climatologies resolving horizontal scales >1000 km can be obtained even with data from a single RO receiver. RO based climatologies have the potential to improve modern operational climatologies, especially in regions where the data coverage and/or the vertical resolution and accuracy of RO data is superior to traditional data sources.

Lower Stratospheric Temperatures from CHAMP RO Compared to MSU/AMSU Records: An Analysis of Error Sources

A comparison of lower stratospheric temperatures (TLS) from (Advanced) Microwave Sounding Unit (MSU/AMSU) records with CHAMP radio occultation (RO) data was performed for September 2001–December 2006. Synthetic TLS temperatures were calculated by applying global weighting functions to monthly RO temperature climatologies and alternatively by applying the RTTOV_8.5 radiative transfer model to the individual CHAMP RO profile data set. The results published by Steiner et al. (2007) showed very good agreement of CHAMP TLS anomalies with MSU records from the University of Alabama in Huntsville (UAH, USA) and from Remote Sensing Systems (RSS, USA) for intra-annual variability. Statistically significant trend differences of UAH and RSS with respect to CHAMP TLS anomalies were found in the tropics (–0.40 K/5 years to –0.42 K/5 years). In this context error sources regarding the retrieval of RO data, the building of climatologies, and the related synthetic MSU computation procedure were analyzed and found to be of minor importance. In the NH extratropics the TLS specific sampling error showed a significant negative trend which is projected globally but tropical trends are small. In total, the contribution of errors from RO was found to be about an order of magnitude smaller than the trend differences and thus insufficient to account for them, especially in the tropical region. Their resolution, currently pursued in a further study, requires either the presence of currently unresolved biases in the MSU records or additional, so far overlooked, sources of error in the RO TLS record. SAC-C, GRACE, and COSMIC TLS temperatures were found to closely match CHAMP temperatures. The results underpin that inter-comparison of independent estimates of the same variable from different instruments is beneficial for the detection of residual weaknesses in otherwise high quality climate records.

Climatologies Based on Radio Occultation Data from CHAMP and Formosat-3/COSMIC

Radio Occultation (RO) data using Global Navigation Satellite System (GNSS) signals have the potential to deliver climate benchmark measurements, since they can be traced, at least in principle, to the international standard for the second. The special climate utility of RO data arises from their accuracy and long-term stability due to self-calibration. The German research satellite CHAMP (CHAllenging Minisatellite Payload for geoscientific research) provided the first opportunity to create RO based climatologies over more than 6 years. Overlap with data from the Taiwan/US Formosat-3/COSMIC (Formosa Satellite Mission 3/Constellation Observing System for Meteorology, Ionosphere, and Climate, F3C) mission allows testing the consistency of climatologies derived from different satellites. We show results for altitude- and latitude-resolved seasonal zonal mean dry temperature climatologies. Our results indicate excellent agreement between RO climatologies from different F3C satellites: After subtraction of the estimated respective sampling errors, differences are smaller than 0.1 K almost everywhere in the considered domain between 8 km and 35 km altitude. Mean differences (over the same domain) are smaller than 0.03 K in any case and can be as small as 0.003 K. Differences between F3C and CHAMP are only slightly larger. The assimilation of RO data at ECMWF (European Centre for Medium-Range Weather Forecasts) considerably improved operational analyses in regions where the data coverage and/or the vertical resolution and accuracy of RO data is superior to traditional data sources.

Correction to “Atmospheric temperature change detection with GPS radio occultation 1995 to 2008”

Citation: Steiner, A. K., G. Kirchengast, B. C. Lackner, B. Pirscher, M. Borsche, and U. Foelsche (2010), Correction to “Atmospheric temperature change detection with GPS radio occultation 1995 to 2008,” Geophys. Res. Lett., 37, L03704, doi:10.1029/2010GL042427. [1] In the paper “Atmospheric temperature change detection with GPS radio occultation 1995 to 2008” by A. K. Steiner et al. (Geophys. Res. Lett., 36, L18702, doi:10.1029/2009GL039777), Figure S7 of the auxiliary material is incorrect and the corrected version appears here.

The GPS radio occultation record – a novel dataset for atmospheric change detection

Fig. 1: Radio signals from a GPS satellite are received onboard a LEO satellite such as CHAMP. An occultation occurs whenever a GPS satellite sets (or rises from) behind the horizon and is occulted by the Earth’s limb as viewed from the receiver. The relative movement of the satellites provides a scan through the atmosphere. Inserts illustrate a retrieved RO CHAMP temperature profile for a particular RO event (A), a distribution of RO events in February 2004 (B), and a monthly mean temperature field for February 2004 (C). TRANSMITTER A